Clowes said it's believed the pair were not left behind by their tour group and added that a full investigation into a timeline of the tragic events would be taking place.

Police do not yet know whether the teenagers knew how to swim, but that would form part of their inquiries.

He said it was important for people to know their abilities and be aware there is always inherent risk in entering the water.

"We're in a nation surrounded by water, there's obviously a lot of concerns and safety issues that we have around that, we manage that as a country, there's nothing specific that I'm aware of in relation to Lake Mackenzie."